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(No Mndel.) 2 Sheets-Sheet 1.

' C. E. SORIBNER.

MULTIPLE `SWITCH BOARD SYSTEM. No. 442,143. Patented Deo. 9, 1890.

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(No Model.)

C. E. SGRIBNER. MULTIPLE SWITCH BOARD SYSTEM.

No. 442,143. Patented Deo. 9,1890.

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CHARLES E. SCRIBNER, OE CHICAGO, ILLINOIS, ASSIGNOR TO TIIE \\'ESTERN ELECTRIC COMPANY, OE SAME PLACE.

NIU LTIPLE-SWITCH-BOARD SYSTEM.

SPECIFICATION forming part of Letters Patent No. 442,143, dated December `9, 1890.

Application filed October 15, 1888. Serial No. 288,140. (No model.)

To all whom it may concern:

Be it known that I, CHARLES E. SCRIBNER, a citizen of the United States, residing at Chicago, in the county ot' Cook and State of Illinois, have invented a certain new and useful Improvement in Multiple-Switch-Board Systems, (Case 175,) of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawio ings, forming a part of this specification.

In inultiple-switch-board systems of telephone -eXehange, single-wire telephone-circuits and metallic telephone-circuits have been hereto used upon the same switch-boards and 'various means have been employed for enabling the operator at one board to test any wire called for to determine whether the line is busy.

My invention herein relates more especially to the operators apparatus, and by its use the circuits are simplified. The metallic circuits are balanced, so as to avoid the effects of induced currents from other circuits. The test for all lines,whether metallic or grounded, is made uniform, whilethe single ol grounded circuit lines may be extended to forni metallic circuits without disturbing` the connections upon the switch-board with the springjack switches.

A feature ol this invention consists in the discovery that the introduction of a retardation-coil into a ground branch extended from one side ot a metallic circuit entirely overcomes the, harmful effect of such ground branch by preventing the flow of the induced currents, which would otherwise create a noise in the telephone.

In my system as hereinafter described each metallic circuit consists of two branches, one branch normally extending from ground at the subscriber-s station, through the gener-` ator and bell to the telephone switch, and thence to the central station, where it is connected through the spring and contact of a different switch on each of the switch-boards and from the contact of the switch on the last board through an individual annunciator to ground. The other branch extends from a contact near the telephone-switch, through 5o the telephone at the subscribers station and thence to the ring or test-piece of the several switches through which the other branch is connected. The single orgrounded telephonecircuits extend each from ground at the subscribers station, in the usual manner, to the central station through a spring and contact ot a diiterent spring-jack switch on each of the boards and from the contact of the switch on the last board through an annunciator to ground. The rings or test-pieces of the springjack switches are connected together by a test-wire which is grounded through high resistance-say five hundred ohms. At each switch-board I provide pairs ot loop-plugs, a test-plug, a telephone, and generator, in connection with switching apparatus arranged tor receiving the subscribers orders, testing-lines called for, and making the connections and disconnections between the lines. The strand of each pair of cords connecting the sleeves ot' the plugs of the pair I connect through a self-induction coil of, say, six hundred ohms resistance, and wound with, say, ten thousand convolutions of No. 32 copper wire through a test-battery, which may be a storage-battery of, say.ten volts to ground. The other strand of each pair-that is to say, the strand connecting the Atips ot' the plugs-is connected through a sel t-in d uction coil oi' the same resistance and wound in the saine manner to ground. When two lines are looped together in metallic circuit', the opposite sides ot` the meytallic ,circuit thus formed will therefore be connected to ground on one side through a seltinduction coil only and on the other side through a self-induction coil and test-battery- In connection with each pair ot cords I provide a switch by means of which the telephone, which is included in a normally-open ground-circuit, may be connected by a haltconnection with the strand ot' the cord connecting the tips. In order that the balance ot the dilterent sides ot the metallic circuits may be maintained, I provide a dummy telephone set. in a normallyopen ground-circuit so arranged that when connection is made from the strand connecting the tips through the regular telephone set another connection will be made from the strand connecting the sleeves through the dummy telephone set to ground. As the dummy set I preferably use a regular microphoneinduction coil and a self-induction coil having the same number of convolutions and the same amount of iron as are used in the telephone, in order that the dummy set may have the same self-inductive eects as the regular telephone set. The strand connecting the sleeves of each of all the pairs of cords on the different boards may be connected with the same test-battery.

In the accompanying` drawings, which are illustrative of my invention, Figure l is a diagram showing three telephonelinestwo metallic and onesingle--connected with three switch-boards and an operator-s outfit at two of theboards. Fig. 2 is a detailed view illustrative of a pair of cords and loop-plugs and the connections with the different strands thereof to ground through the self-induction coils, together with the switch for connecting and disconnecting the telephone set and the corresponding self-induction and induction coils with the different strands, the test-plug and its circuit through one coil of an induction-coil, the other coil including` the telephone, the test-battery, and a connection therefrom leading to a second pair of cords. Fig. 3 is a detailed sectional view of one of the loop-plugs.

Like parts are indicated by similar letters and figures of reference throughout the different figures.

Subscribers station l in Fig. l is connected with the switch-boards l, 2, and 3 at the oentral office by a metallic circuit a., consisting of two branches or limbs a a?. The normal circuit ofY limb a may be traced from ground at subscribers station l, through the generator and bell at said station to the telephoneswitch, and thence, as shown, to the central office, and-thence through the spring and contact of switches b b2 h3 on the different switchboards, and from the contact of the switch b3 on the last board, through an individual annnnciator c, and thence to ground. The circuit of the limb or branch a2 may be traced normally from a contact-point near the telephonesswitch of station l, through the telephone at said station, and thence, as shown, to the cent-ral office to the test-pieces or insulated tubes of the series of switches b b2 b3. The metallic circuit as thus traced is old and well known. The single or grounded telephoneline CZ extends in the ordinary way from subscribers station 2 to the central office, and thence through switches e', e2, and eS-one on each of the switch-boards-and from the switch on the last board through an individual t gle line is provided with a connection or terminal on each of the switches of the line, the terminals or test-pieces being normally open, the test-circuit being provided, however, witha permanent ground-connection through high resistance. The connection to ground through high resistance is a novel feature of my invention.

The metallic circuit h of station 3 is connected with switches t" 213, and through an annunciator 7c in the same manner heretofore described with respect to the circuit of station l. At each of boards l and 3, I have shown an operators outfit. At board l the telephone-lines a d are shown looped together. At board 3 connection has been made with switch 3 of line h, andthe test-plug is shown touching the test-piece of switch b3, as if the subscriber 3 had called for subscriber l, and the operator, having received the call, was in the act of testing to find out whether the line of subscriber l was in use. As line dof subscriber l is connected with line d ot' subscriber 2 at board l, the operator testing at board 3, as shown, will liud the busy-test indicated.

In Fig. 2 I have shown an operators outfit in det-ail in the position indicated at board 3, Fig. l.

I will describe the operators outfit shown in Fig 2 in detail. The loop-plugs ZZ are of the form shown in Fig. 3, and are connected by a pair of flexible cords. Strand ml connects the insulated sleeves of the two loop-plugs together, while the tips of said plugs are conneet-ed together by means of strand n. .A branch m extends from strand n through self-induction coil m2 and test-battery m3 to ground. From the strand n, which connects the tips, a branch n extends through a selfinduction coil n2 to ground. Thus we have from each of the strands of the cords connecting loop-plugs Z Z, a branch connection to ground, andin each of these branches is included a self-induction coil, the branch from the strand connecting the sleeves after passing through its self-induction coil m2 being connected through a test-battery m3. These self-induction coils n2 and m2 should be of the saine construction, in order that theirsclf-inductive effects will be the same upon the different sides of a metallic circuit formed when two metallic telephone-lines are looped together by means of the loop-plugs l Z.

The operators telephone o is'connected in branch wire 0 with the strand n, which connects the tips of the lloop-plugs. This branch 0 includes spring 02 and telephone-contact 03 of a loop-switch, and after passing through the telephone set is connected with ground.

To balance the self-inductive effects of the telephone set o, I provide a branch j) from the strand u, connecting the sleeves of the plugs, which branch p extends through spring p and contact p2 through a self-induction coil p3 and an ordinary microphone-induction coil p4 to ground. Thus whenever the telephone o is connected with the strand n, as shown in Fig. 2,a branch j) is closed to the 'other strand 'n of the cords through apparatus 193294, having the same self-inductive caA pacity as the telephone set. Bridged across IOO IIO

the ltelephone is a wire q, including a winding of the converter or induction-coil q. Test-plug q2 is simply an ordinary terminal which is provided with a single connection or strand qs, which includes the other winding ot converter q and extends to ground.

It is evident that the presence of a vibratory or pulsatory current upon wire rf will be indicated to one listening at the telephone o. IVire Ir, connecting between self-induction coil m2 and battery m3, is simply a connection with a strand of another pair of cords. There may be, for example, twenty pairs of cords at each switchboard. I will not specically describe the clearing-out annunciator, the calling-keys, and the generator connections, since they are old and their operation understood by those having any knowledge of telephone-exchange apparatus.

The operators apparatus at board 3, Fig. l, is lettered to correspond with the saine apparatus in Fig. 2. The operators apparatus at board I of Fig. l is the same,though shown in a different position. At board 3 the telephone 0 is in circuit, while at board l the telephone-circuit is open at the loop-switch s, the plunger of said switch s being forced down so as to lift the springs of said switch from their contacts. The testplug s is resting in its socket, while the two loop-plugs s2 s3 are shown inserted in the spring-jack switches e b', so as to loop the telephonelines a and d together.

IVhen any two lines are connected together, whether metallic or single or a metallic circuit with a single circuit, as shown, the testbattery m3 will be connected to the test-pieces to all the springjack switches of the two connected lines. In case of metallic circuits it is essential. that the connection with the test-battery be through a self-induction coil, and it is especially desirable, though not essential, that the other branch or limb of the circuit be provided with a corresponding branch ground-connection through a self-induction coil of the same character, in order that there may be a balance between the different sidesof the metallic circuit. When the operator connects his telephone to one side of a metallic circuit, it is also desirable that a corresponding connection be made with the opposite side of the metallic circuit, in order that the balance with respect to inductive effects may be maintained.

The steps or motions of the operator in receiving a call, testing the line called for, coinpleting the connections, and disconnecting the lines when the subscribers are done talking are briefly as follows: The individual annunciatordrop, as 7s, falls. The operator atonce inserts the answering loop-plug Z in the spring-jack switch of the corresponding line and brings the telephone 0 into circuit and receives the order. Thereupon the test is made of the line called for by applying terminal q2 to the test-piece ot' the spring-jack switch of the line thus required. If thc line is busy, the test-pieceof the spring-jack switch tested will be connected with battery and current from said battery will be sent over wire qs, which will cause a sound in the telephone 0. This will be notice to the operator that the line tested is busy, and the calling subscriber will be notified to wait. If, however, there is no sound in the telephone when the test is made, the operator will know that the line wanted is idle and will at once complete the connection by inserting the other plug of the pair, as Z', in the spring-jack switch of the line. The connections will then be complete, and the called subscriber will be notified by current sent from the generator over his line. The clearing-out signal is received upon a clearing-out annunciator included in the strand connecting the tips of the plugs. The operator, seeing the clearingout drop fall, listens to make sure that the subscribers are through, and then simply pulls out the loop-plugs.

It will be observed that the balance is maintained during the entire time that the two lines are connected.

My invention adxnits of various modications that would readily suggest themselves to those having any special knowledge of telephone-exchange apparatus, and I therefore do not limit myself to the details of construction shown.

Having thus described my invention, I claim as new and desire to secure by Letters Patentl. The combination, with metalliccircuit telephone-lines looped together in metallic circuits by a pair of loop-plugs and iiexible cords, of a branch circuit to ground from the strand connecting the sleeves of the plugs,

`said branch including a self-induction coil and a battery, said telephone-lines being connected each with different switches on each of two or more switch-boards, and the sleeves of said plugs being connected, respectively, with the test-pieces of the switches of the re-4 spective lines, whereby the test-battery is connected to said test-pieces, while the iiow of induced currents upon the metallic circuit is prevented, substantially as described.

2. The combination, with a telephone-line connected with switches distributed 011 different switch-boards, of test-pieces, one on each switch,tne test-pieces being permanently connected together by a wire connected through resistance, of a loop-plug inserted in one of said switches, the tip of said plug lifting the spring of the switchin which it is inserted and forming contact therewith, while the sleeve of said plug is connected with the test-piece of said switch, a branch circuit to ground from the strand of the cord connected with the tip of the plug, and a selt`-induction coil and battery included in said groundl branch, substantially as and for the purpose specilied.

l 3. A pair ot" loop-plugs and flexible cords adapted to connect two telephone-lines to- IOO IIO

gether, in combination with a branch circuit from one of said strands through a self-induction coil and battery to ground, and a corresponding branch circuit to ground from the other strand through a corresponding selfinduction coil, substantially as described.

4. The combination, with a metallic-circuit telephone-line extending from a subscribers station to a spring-jack switch at the central station, of a loop-plug inserted in said switch, a liexible cord having two strands connected with the different terminals of said plug, the operators telephone-outfit, and a corresponding dummy outfit, and a switching device whereby the telephone-outfit andthe dummy ontiit may be connected to the different strands ot' the cords, substantially as described.

5. The combination,with the two strands of a flexible cord, each strand beingprovided with a permanent ground-connection, of two branch circuits to ground connected with the difterent strands of the cord, one branch containing a telephone and the other branch containing a corresponding self-induction coil, and a switching device whereby the telephone and the corresponding self-induction device may be connected at the same time with the different strands, respectively, of the cord.

6. In a telephone-exchange apparatus, a pair of cords provided with terminal loopplugs adapted to form connections between the telephone-line terminals, of a permanent branch connection from one of the strands ot said cords through a self-induction coil and a battery to ground, substantially as and for the purpose specified.

7. The combination, with a metallic circuit a, extending from asubscrbers station to the central oiiice and being there normally connected with several spring-j ack switches b b2 b3 on dierent switch-boards,of a single telephone-line circuit d, extending from its subscribers station to the central office and being there connected with several spring-jack switches e e2 e3 on different switch-boards, the test-circuit g, connected with the insu- Alated frames or t-est-pieces of said switches c e2 e3, said test-circuits being connected thron gh resistance g to ground, a pair of loop-plugs s2 s3 and their cords connecting said telephonelines together upon one of the switch-boards, a testbattery, and a self induction coil branched to the strand of the cord connecting the sleeves of the plugs, and a currentindicating device at another board adapted io be connected to the test-ring of either ot' the switches .of said line, whereby it may be determined whether either of said lines is in use.

8. The combination, with a metallic circuit c, extending from a subscribers station to the central office and being there normally connected with several spring-jack switches h b2 b3 on different switch-boards, ot` a single telephone-line circuit CZ, extending from its subscribers station to the central office and beingthere connected with several spring-jack switches c c2 c3 on diiierent switch-boards, the test-circuit g, connected with the insulated frames or test-pieces of said switches e e2 e3, said test-circuits being connected through resistance g to ground, a pair of loop-plugs s2 33 and their cords connecting said telephonelines together upon one of the switch-boards, a test battery, and a self induction coil branched to the strand of the cord connecting the sleeves of the plugs, a corresponding branch to ground from the other strand of the cord, includingacorresponding self-induction coil, and a current-indicating device at another board adapted to be connected to the test-ring ot' either of the switches of said line, whereby it may be determined whether either of said lines is in use.

9. The combination, with a metallic circuit c, extending from a subscribers station to the central office and being there normally connected with several spring-jack switches b b2 b3 on different switch-boards, of a single telephone-line circuit CZ, extending from its subscribers station to the central oiiice and being there connected with several spring-jack switches e e2 e3 on different switch-boards,

the test-circuit' g, connected with the insug lated frames or test-pieces of said switches e e2 e3,said test-circuit being connected through resistance g to ground, a pair ot loop-plugs S2 S3 and their cords connecting said telephonelines together upon one ot the switch-boards, a test battery, and a` self induction coil branched to the strand of the cord connecting the sleeves of the plug, and a corresponding branch to ground from the other strand of the cord, including a corresponding seltinduction coil, substantially as and for the purpose speciiied.

10. The combination, with two metallic telephone-line circuits looped together at one of several multiple switch-boards with which said lines are connected, ot' a branch circuit from the side of the united circuit, said lines connected with the test-pieces of the switches, said branch'including a self-induction coil and battery, and a' corresponding branch circuit to ground from the other sidel of said metallic circuit through a corresponding self-induction device, whereby the said circuit is balanced with respect to inductive effects, substantially as and for the purpose specified.

ll. The combination, with an operators telephone and switching apparatus, ot a bridge-wire q between the terminals ot said telephone, said bridge-wire containing one coil of a converter, and a ground-circuit g3, including the other coil of said converter and provided with a movable terminal q2, substantially as shown and described.

12.7The combination, with the telephone connected with a strand of a flexible cord in the united circuit of two telephone-lines, of a converter with one of its coils bridging said telephone, a circuit provided with a movable terminal, including the other coil of said converter, and a test-terminal of another telephone-line, to Which said movable terminal is applied, substantially as and for the purpose specified.

13. The combination, with a telephone-line connected with switches on diierent switchboards, the switches of said line being provided with test-pieces permanently connected together, of a loop-plug inserted in one of the switches of said line, one point or `terminal of said plug being connected with the spring or line terminal of the switch and the other point or contact ot said plug connected with the testpiece of said switch, the strand ot the cord connecting' with the terminal of the plug which is closed to the test-piece of the switch being branched through a selfinduction coil and battery to ground, substantially as and for the purpose specified.

il. The combination, With several pairs of cords and their loop-plug terminals, of telephone-lines each connected with two or more spring-jack switches distributed on different switch-boards, the test-pieces of the switches ot the different lines respectively being permanently connected together, the terminals of the different loopplugs being adapted to close the one to the line terminal or spring' of the switch in which it is inserted and the other terminal to the test-piece ot the switch and a battery branched through different self-induction coils to the strand of each of the pairs of cords, which strand connects with the terminals of the plugs Which close upon the test-pieces of the switches, whereby a common battery suppliesvcurrent for many test connections.

In Witness whereof I hereunto subscribe my name this 10th day of October, A. D 1888.

' CHARLES E. SCRIBNER. \Vit11esses CHAS. G. HAWLEY, GEORGE P. BARTON. 

